1. Field of the Invention
The present invention relates to antennas, and more particularly relates to an on-board antenna used for receiving terrestrial television broadcast signals, etc.
2. Description of the Related Art
A conventional on-board antenna 50 for receiving terrestrial television broadcast signals is shown in FIG. 7. This conventional antenna 50 includes a rod-shaped radiation conductor 51 which is adjusted so as to resonate at a desired frequency. The angle between the radiation conductor 51 and a pedestal 52 is freely adjusted by using a supporting portion 53, which functions as a fulcrum. As shown in FIGS. 8A and 8B, this antenna 50 is attached on a rear window 61 or on a roof 62 of a vehicle 60.
Generally, to solve the problem of fading, which particularly occurs when signals are received by a moving antenna, a diversity receiving system is adopted in vehicles. In this system, a plurality of the antennas shown in FIG. 7 are used, and one of the antennas which exhibits the highest receiving level is selected.
With respect to the conventional antennas as described above, the operational bandwidth of a single antenna is not sufficiently wide. Thus, when a wide bandwidth must be covered, as in a case of receiving television broadcast signals, multiple antennas having different operational bandwidths are prepared. In addition, external circuits such as tuning circuits and amplifying circuits are attached. Accordingly, there has been a problem in that a considerably high total cost is incurred to obtain a wide operational bandwidth. In addition, since a plurality of antennas, each of which is relatively large, is used, the antennas are necessarily attached to the exterior of the vehicle. Thus, there are risks in that the antennas will be damaged or stolen. In addition, there is a problem in that the appearance of the vehicle is degraded.